1. Field of the Invention
The present invention relates to a dielectric thin film element for a piezoelectric actuator using a dielectric thin film, a piezoelectric actuator and a liquid discharge head, and a method for manufacturing the same. The dielectric thin film element of the present invention can be applied to not only piezoelectric actuators used for a liquid discharge head but also various sensors, non-volatile memories and capacitor insulating film for DRAM.
2. Related Background Art
A thin film material recently attracting attention is a dielectric material having a perovskite structure constituted by the formula ABO3. Since the material has excellent ferroelectric property, pyroelectric property, piezoelectric property and dielectric property as represented by Pb(Zr,Ti)O3, application to piezoelectric actuators for liquid discharge heads, microphones, sounding bodies (e.g., speakers), various transducer sensors, non-volatile memories, capacitor insulating film for DRAM is expected utilizing the above characteristics.
To improve the properties of these materials or to achieve integration thereof, formation of thin film is extremely important. For example, further downsizing and high-functioning of piezoelectric actuators by using a piezoelectric thin film has led to the development of applications to micromachines, microsensors and liquid discharge heads, and it is expected that micro-size and accurate handling can be achieved in various fields, which has been considered impossible.
In the case of a liquid discharge recording apparatus equipped with a piezoelectric actuator using a piezoelectric driving element, a vibrating plate equipped with the piezoelectric driving element is jointed to a flow path substrate having a pressure chamber communicated to a liquid supply chamber such as an ink chamber and a discharge port (nozzle) communicated to the pressure chamber, while the vibrating plate being faced with the pressure chamber. In such construction, by expanding and contracting the piezoelectric driving element by applying a pre-determined voltage thereto, flexibility vibration is induced to compress liquid such as ink in the pressure chamber and droplets are discharged from the discharge port.
At present, color ink jet recording apparatuses have been widely used, but improvement of printing abilities, in particular, high resolution and high-speed printing, are demanded and high resolution and high-speed printing has been attempted by using a multi nozzle head structure which is a micro-processed liquid discharge head. For the microfabrication of the liquid discharge head, downsizing of piezoelectric driving element for discharging liquid is necessary.
Conventionally, a piezoelectric film manufactured by micro-profiling of a piezoelectric body obtained by sintering based on techniques such as cutting and grinding has been used for such compact piezoelectric driving element. Aside from this, research has been conducted to develop a high precision, micro piezoelectric driving element by laminating a piezoelectric body as a thin film and utilizing photolithographic processing technique used for semiconductors. In addition, in view of the high functioning of the element, it is desired that the piezoelectric body is a single crystal or single oriented dielectric thin film, and development of heteroepitaxial growth technique has been extended.
In the technique of heteroepitaxial growth of dielectric thin film, it is important to reduce the misfit of the lattice constant between the base layers including a substrate and the dielectric thin film. A method of inserting an intermediate layer between the substrate and the dielectric thin film for reducing the lattice misfit is general and widely known.
On the other hand, a technique of forming a dielectric thin film having a high single orientation degree has been studied despite that the substrate and the dielectric thin film have no epitaxial relation. For example, as described in Japanese Patent Application Laid-Open No. H07-300397, a method for obtaining a highly oriented piezoelectric thin film by utilizing the difference in the linear expansion coefficient of the substrate and the dielectric thin film has been suggested.
However, in the above conventional epitaxial film forming techniques and a film forming method utilizing the difference in the thermal expansion coefficient of the substrate and the dielectric thin film as represented by Japanese Patent Application Laid-Open No. H07-300397, stress due to the lattice misfit or the difference in thermal expansion coefficient is generated in the dielectric thin film to cause peeling of the film, whereby construction of a large area dielectric thin film element has been prevented.
Even in the case where peeling of the film is not caused, the stress generated in the dielectric thin film leads to deterioration of properties of the dielectric thin film, such as fatigue characteristics of FeRAM, whereby formation of the dielectric thin film element has been prevented.
In particular, since piezoelectric actuators such as a liquid discharge head used for micromachines and ink jet recording apparatuses which have been extensively studied recently and in which the dielectric thin film undergoes displacement have a large film thickness of about 0.5 μm to 500 μm and have piezoelectric displacement, the problem of the peeling of the dielectric thin film from the substrate or the intermediate layer is essential.